The present invention is concerned with a sensor for determining the steer angle, that can be mounted, for example as a commercially available unit, to the steering wheel of an automotive vehicle. Steer angle sensors are required for the yaw angle control of automotive vehicles to prevent a vehicle from steering off, for example, in a slippery bend. Control systems of the afore-described type require awareness of the steer angle of the front wheels momentarily adjusted to determine and control the driving pattern of the vehicle from the angle and other parameters. Sensors of this type, frequently are provided with a code disk coupled to the steering wheel at least indirectly so that the position of the steering wheel can be directly read from the associated codes on the code disk. The way of operation of a code disk of the afore-described type has already been described by 195 32 903.1. Code disks of this type operate with a relatively high precision which is required for an accurate control. Conversely, it is desirable to integrate the scanner of the steer angle sensor into the printed circuit board of the sensor to attain a simple and inexpensive design. Moreover, it is important for the spaces between the scanner and the code disk carrying the code to be precisely maintained to avoid erroneous values. A possibility to achieve this, resides in combining code disk and scanner in one unit and to assemble the same in the housing as a complete set. However, this measure involves comparatively great efforts. If the code disk alone is pivotally arranged on a mounting plate of its own to be then assembled in the housing it should, in addition, be noted that the tolerances of base plate and printed circuit panel or mounting plate of the scanner will add up.
It is the object of the invention to mount the components and units required for the sensor in a simple and inexpensive way within the appertaining housing. The code disk is arranged within the housing in a directly rotatable way, thereby enabling a highly precise adjustment of the code disk. The present invention is particularly beneficial in applications where the position of the code disk must be accurately adjusted by a precise orientation of the code disk drive over a driving tongue because the position of the housing is determined by the forced position of the code disk. To clearly associate the position of the scanner to the code disk the scanner is inserted into a socket rigidly connected to the housing. This clearly couples the scanner to the housing. Also, the position of the code disk relative to the scanner and the housing is fixed as both of them are directly connected to the housing.
Due to the position on the steering wheel directly or indirectly actuating the code disk, on the one hand, the position of the housing of the sensor module is predetermined, while, on the other hand, the steering pillar extending to the steering wheel must be given space in order to establish the connection between steering column and steering rod linkage. To insure short distances between the drive and the bearing of the code disk, it is, therefore, especially favorable to provide the bearing marginally of the passage opening of the steering pillar through the housing. To that extent, an annular wall is mounted marginally of the passage opening within the bottom of the housing, with the said wall holding the lid face of the code disk at a space from the housing bottom so that space will be provided for the code toothing preferably extending axially from the lid face of the code disk to the housing bottom. Conversely, the position of the code disk is clearly fixed with respect to the housing bottom as the spring struts resiliently hold the code disk in engagement with the annular wall of the housing bottom. To prevent the code disk from getting lost from the housing bottom, during introduction of the code disk into the housing bottom, the spring struts are deflected through the annular wall until they engage the locking hooks thereof, with the edge of the spring wall. The spring struts, in relaxed condition, preferably extend in parallel to the axis of rotation of the code disk and only during assembly are slightly deflected to provide space for the locking hooks to enable them to pass through the circular opening.
The groove toward the housing bottom and toward the circular hole is open thus being of an L-shaped contour circumferentially extending along the housing bottom. To insure a simple configuration both of the locking connection of the code disk within the housing and of the drive of the code disk, the code disk includes a circular hole slightly smaller that that of the housing bottom so that the spring struts extend in parallel to the inner surface of the annular wall facing the opening. However, it is not only the spring struts that emerge from the edge of the code disk opening, but support walls of approximately equal height are standing upright thereon to carry ears through which the code disk is at least indirectly actuated by the steering wheel.
To simply center the optical scanner over the teeth of the code disk forming the coding, the components of the scanner are adjusted in a common socket with respect to one another and, hence, through the housing bottom, also with respect to the coded teeth of the code disk. The tape elements of the scanner are, therefore, firmly centered with respect to one another through the bays associated thereto and are optically coupled to one another through the slots extending into the grooves. The square coding teeth then annularly move in series within the said groove track, with the teeth being scanned, thereby determining the position of the code disk.
In order to enable the printed circuit board of the code disk to be loaded on both sides, stepped centering pins are provided on the housing bottom. This will especially apply if the scan elements of the scanner are integrated into the printed circuit board. Conversely, the distance of the printed circuit board from the housing bottom provides the required space in order to enable the printed circuit panel to be loaded, if need be, on both sides. In practice, it has proved advantageous to load one side of the printed circuit board and to solder, on the opposite side, the connections to the conductor lines on the printed circuit panel. In that case, the contact pieces and the contact ring of the stepping switch (see EM 95/364) are located on the same side on which the contact points are to be soldered. If the socket of the scanner is to be designed as a separately mounted unit to enable easy replacement or adjustment during assembly, a bay is formed in the housing bottom as also in that case a firm association between the position of the scanner and the position of the code disk within the housing is permitted.